1. Field of the Invention
The present invention relates to air entrainment nebulizers and more particularly concerns a nebulizer that provides a range of high oxygen content with optimum total output flow rate.
2. Description of Related Art
In common forms of inhalation therapy, an oxygen enriched air mixture is provided for introduction into a patient's lungs by means of suitable breathing apparatus. The gas mixture is preferably moisturized and transmitted to the patient through a flexible tube which may be several feet or more in length. The nebulizer provides a gas stream that entrains water particles rather than water vapor (as in a humidifier). Minimum water particle size is required to ensure that water will reach deeper portions of the respiratory tract. A nebulizer is used to provide a gas mixture that may be selectively varied from a high oxygen content, nearly 100% in some cases, to as little as 28%. A nebulizer with a wide range of oxygen percentages is described in U.S. Pat. No. 4,767,576 entitled "Nebulizer With Auxiliary Gas Input". In the arrangement of this nebulizer, pressurized oxygen is fed to a mixing chamber through a first nozzle and pressurized air is fed to the mixing chamber from a second nozzle so that the total flow rate, e.g. the flow rate of oxygen and the flow rate of air, can be readily controlled. Therefore, by controlling flow rate of both pressurized gaseous inputs to the mixing chamber, the total flow rate that is discharged from the nebulizer can be readily controlled. Flow rates of the oxygen and pressurized gas are controlled by metering valves on the input tubing, as is well known. The nebulizer with the auxiliary gas input, although effective for its purpose, is not useful where a pressurized auxiliary air source is not available. In some hospitals and similar facilities, only pressurized oxygen outputs are provided so that a nebulizer with the auxiliary gas input as described in U.S. Pat. No. 4,767,576 cannot be employed.
A nebulizer that uses solely a pressurized oxygen input depends upon air entrainment for auxiliary gas or air input as is described, for example, in U.S. Pat. No. 4,629,590 for "Nebulizer." In the nebulizer of U.S. Pat. No. 4,629,590, pressurized oxygen is fed through a jet that produces a lowered pressure for entrainment of water from a container which is thus drawn into a mixing chamber having a pair of apertures that are adjusted by a rotating sleeve. The nebulizer of U.S. Pat. No. 4,629,590 employs an oxygen jet capable of flowing up to about 15 liters per minute of oxygen and achieves adjustment of oxygen content of the discharged mixture by varying the air entrainment apertures in the mixer body. However, oxygen content above about 60% of the output mixture cannot be obtained with the air entrainment nebulizer of U.S. Pat. No. 4,629,590 without providing an unacceptably low total output flow rate. This nebulizer is provided with a limited oxygen flow rate jet and thus is not capable of producing high flow rates of oxygen. However, even if it should be used with an oxygen jet capable of higher oxygen flow rates, much greater quantities of air are pulled into the mixing chamber through the air entrainment ports and thus total output flow rates well over 100 liters per minute or sometimes as high as 140 or 150 liters per minute would be provided if a larger oxygen jet were used to flow 30 or 40 liters per minute of oxygen to the mixing chamber. Also, though the nebulizer with the auxiliary gas input can provide high oxygen percentages at optimum flow rate, this instrument can be used only where there is a source of auxiliary gas input. The nebulizer of U.S. Pat. No. 4,629,590, on the other hand, can be used wherever there is solely a source of pressurized oxygen and is not dependent upon the availability of pressurized auxiliary gas. However, this nebulizer can provide output mixtures having only limited (not more than about 60%) percentages of oxygen with useful total flow rates.
In fact, where an air entrainment nebulizer of the type shown in U.S. Pat. No. 4,629,590 is employed, high oxygen content (above about 60%) at useful flow rates (e.g. between about 40 to 70 liters per minute) can be achieved only by employing two similar nebulizers of this type and combining their outputs by a tubing "Y" connection. This is so because when such an air entrainment nebulizer is adjusted for an oxygen percentage above 60%, its air intake is so restricted that its total output flow rate is too small to be useful without being combined with output of a second similarly adjusted air entrainment nebulizer. With the air entrainment nebulizer of U.S. Pat. No. 4,629,590, even with limited total output flow rates, the instrument may be subject to back pressure in the order of 3 to 5 cm of water when the patient either is exhaling or is between breaths. Such back pressures tend to cause the water droplets that are swirling around the mixing chamber to be projected outwardly through the air entrainment openings, thereby causing an undesirable "spitting" which degrades operation of the nebulizer.
Accordingly, it is an object of the present invention to provide an air entrainment nebulizer that avoids or minimizes above-mentioned problems.